SITE, a group which examines Islam extremists, said new convert Thompson posted Facebook rants describing jihad as “a justifiable response to the oppression of the Zionists and the Crusaders”.

Gunned down: Zale Thompson

Another alleged post read: “Helicopters, big military will be useless on their own soil. They will not be able to defeat our people if we use guerilla warfare.” Police commissioner William Bratton said they were trying to establish a motive but did not rule out terrorism.

The brother of a British jihadist killed fighting in Syria has appeared in court charged with planning to travel to the war-torn country. Tuhin Shahensha, 26, of Southsea, Hants, was remanded in custody at Westminster magistrates court to appear at the Old Bailey.